Method of making a rotor for an electric device

ABSTRACT

A process for producing a cylindrical rotor for a DC motor. A flexible insulative film is provided having a number of mutually insulated regularly spaced parallel conductors on one surface thereof, the conductors extending generally parallel to opposite longitudinal edges of the film. The film, which may be conveniently provided in sheet or rolled strip form, is cut along two parallel lines intersecting the longitudinal edges at an acute angle to provide a parallelogram shaped section in which the conductors terminate flush with the cut edges of the parallelogram. The parallelogram is folded back on itself with the conductors on the outer surface to obtain a trapezoidal folded sheet with the conductor ends lying on a single edge of the trapezoid. The trapezoidal folded sheet is rolled to obtain a cylinder, and the ends of corresponding conductors joined by soldering operation to produce the finished rotor. A modified process contemplates dispensing with the folding operation, and forming the trapezoidal sheet from a plurality of parallelograms; the length of the individual parallelograms being stepwise increased by means of changing the angle at which the parallelograms are cut from the film.

United States Patent [1 1 Ishikawa METHOD OF MAKING A ROTOR FOR AN ELECTRIC DEVICE [75] inventor: Kazuo Ishikawa, Yokohama, Japan [73] Assignee: Jeco Co., Ltd., Tokyo, Japan [22] Filed: June 4, 1973 [21] Appl. No.: 366,779

Related U.S. Application Data [62] Division of Ser. No. 187,802, Oct. 8, 1971,

abandoned.

[30] Foreign Application Priority Data Oct. 12, 1970 Japan 45-89462 [52] U.S. Cl 29/598, 310/265, 310/266 [51] Int. Cl. H02k 15/04 [58] Field of Search 29/598, 625; 310/154, 265, 310/266, 268, 195

[ I Jan. 7, 1975 Primary Examiner-Carl E. Hall Attorney, Agent, or FirmWolfe, Hubbard, Leydig, Voit & Osann, Ltd.

[57] ABSTRACT A process for producing a cylindrical rotor for a DC motor. A flexible insulative film is provided having a number of mutually insulated regularly spaced parallel conductors on one surface thereof, the conductors extending generally parallel to opposite longitudinal edges of the film. The film, which may be conveniently provided in sheet or rolled strip form, is cut along two parallel lines intersecting the longitudinal edges at an acute angle to provide a parallelogram shaped section in which the conductors terminate flush with the cut edges of the parallelogram. The parallelogram is folded back on itself with the conductors on the outer surface to obtain a trapezoidal folded sheet with the conductor ends lying on a single edge of the trapezoid. The trapezoidal folded sheet is rolled to obtain a cylinder, and the ends of corresponding conductors joined by soldering operation to produce the finished rotor. A modified process contemplates dispensing with the folding operation, and forming the trapezoidal sheet from a plurality of parallelograms; the length of the individual parallelograms being stepwise increased by means of changing the angle at which the parallelograms are cut from the film.

6 Claims, 12 Drawing Figures Patented Jan. 7, 1975 3.858309 6 Sheets-Sheet 1 INVENTOR XXIX/d f/i/MM TTORNEY Patented Jan. 7, 1975 6 Sheets-Sheet 2 vEN'ro R fl/ Aff/ Patented Jan. 7, 1975 v ,858,309

6 Sheets-Sheet I5 Wit @444 i l/gwzw/ TORNEY Patented Jan. 7, 1975 6 Sheets-Sheet 4 WWW Patented Jan. 7, 1975.

6 Sheets-Sheet 6 (9 Pg 6 G? 9 S N S N S N S INVENTOR 474/4 fJW/M/V/ ATTOR NEY METHOD OF MAKING A ROTOR FOR AN ELECTRIC DEVICE This is a division of application Ser. No. 187,802 filed Oct. 8, 1971 now abandoned.

This invention relates to a rotor for an electric device, particularly for a cylindrical type DC motor having a hollow cylindrical rotor, and to a process for producing the same.

A hollow cylindrical type motor is already disclosed, for example, in US. Pat. No. 3,191,081. The rotor for the motor of this type lacks the winding core, and the armature consists solely of a coil. Preparation of such a coil requires a special winding machine, and the limited winding speed restricts productivity and makes mass production at a low cost difficult. Besides, since the coil wire must be bent in a sharp angle at the ends, the wire diameter must be small and, therefore, any motor of high torque cannot be produced by this method. Also, a motor utilizing a printed circuit is already disclosed, for example, in Japanese Pats. Nos. 281,556, 292,721 and 292,722. The rotor for the motor of this type is produced by forming a coil on an insulative plate by means of an electroetching process or the like, and a mass-production at a low cost is difficult also in this case since the coil of complicated shape necessitates the preparation of the printed circuit piece by piece by means of the electroetching or the like measures.

This invention is, therefore, to provide a rotor which is free from the above-mentioned drawbacks, enables easier producing process and is thus adapted for largescale mass-production, and further is capable of passing a relatively large current.

This invention will be detailed with reference to the attached drawings, in which:

FIG. 1A is a vertical cross-section of the electric device according to this invention;

FIG. 1B is a similar vertical cross-section of another example according to this invention;

FIGS. 2A, 2B and 2C show an example of the rotor coil;

FIG. 3 is an explanatory view showing the working principle thereof;

FIGS. 4A and 4B and FIG. 5 show other examples of the rotor coil;

FIG. 6 is an explanatory view showing the working principle thereof; and

FIG. 7A and 7B show still another example of the coil.

FIG. 1 shows the vertical cross-section of a motor according to this invention, which comprises a casing 11 made of ferromagnetic material, an annular magnet 12, a magnet holder 13 combining said magnet 12 and said casing 11 working as a yoke integrally, bearings 14 mounted on both extremities of an axial hole provided in said magnet holder 13, a rotar shaft 15 rotatably supported by said bearings 14, a cylindrically formed coil 16 fixed at an end to a coil supporting disk 17 which is fixed at the center to said rotor shaft 15, a cover plate 18, brushes 19 disposed so as to be constantly in contact with the outer periphery of the cylindrical rotor, brush springs 20 and terminals 21.

Although the brushes in this embodiment are disposed to be in contact directly with the conductive wires or elements of the coil 16 without using any commutator, it is also possible to provide a commutator formed on said disk 17 by means of an electroetching process or the like so as to be connected to the coil, as shown in FIG. 1B.

FIG. 2 shows the simplest procedure for producing the coil according to this invention, which comprises steps offorming, as shown in FIG. 2A, a number of parallel conductors (1-1), (2-2), (11-11) with a regular interval or spacing by means of a proper printing process on aflexible plastic sheet of, for example, polystyrene resin sheet, cutting thus obtained printed conductors diagonally and thereby producing a parallelogram abcd provided with two sides which are parallel to said parallel conductors, and folding said flexible sheet along the folding line A A at the center thereof with said printed conductors outside so that the edges of l and n of the side conductors will superpose on each other, thereby obtaining a trapezoid as shown in FIG. 2B. Said trapezoidal sheet is then rolled up as shown in FIG. 2C so as to be a formal uniform cylinder, whereby two isosceles triangles formed by nonoverlapping parts of said sheet on both sides of said trapezoid are exactly superposed on each other.

In FIG. 2A, the extremities of said parallel conductors are numbered from 1 to n, while the other extremities are numbered from 1 to n accordingly. Referring to electric connection action of the parallel conductors for forming the coil, if the parallelogram of FIG. 2A is formed so that the edges 1 and n will superpose on each other when it is folded as shown in FIG. 2B, the isosceles triangle having the conductor edges 1 through (n 1) at the bottom thereofis completely superposed on the other triangle having conductor edges 2 through It at the bottom thereof, when said flexible sheet is rolled up as shown in FIG. 2C.

It is thus possible to make connections between the corresponding ends of said conductors, namely 1 and n, 2 and 1', and n and (n l) in the rolled-up state shown in FIG. 2C by means of a simple operation for example by dipping the lower end of said rolled-up sheet into molten solder. These connections, when completed, form a complete loop for allowing an electric current fed from the edge 1 to flow through all the conductors in the sequence of 1' 2 2' 3 3' (n-2)-(n1)-(n-l)'-n-n-lsoastoreturn to the original edge.

The working principle of the cylindrical rotor thus formed will be explained in the following, with reference to FIG. 3.

FIG. 3 shows the development of cylindrical rotor and magnet to be a plane. Due to the manufacturing process explained above, the rotor, when developed to be a plane, will have conductors which are running diagonally from the bottom in rightward upper direction on the front surface (in the drawing) whereas on the reverse surface from the top in leftward downward direction, that is, in diagonally opposing directions on the respective surfaces. For the purpose of brevity, however, the rotor in said drawing is divided into the representative blocks in each of which the direction of electric current in said conductors is indicated by arrows.

When two brushes 19 for and currents are brought into contact with the coil at an angle of with respect to each other, as in FIG. 1A, the coil can be considered to be composed of two rhombs with vertex thereof at the brush or and four triangles as divided by thick lines in FIG. 3.

In each block the direction of electric current and the current vector composed therefrom are represented by thin and thick arrows, respectively.

The current vector in four triangular blocks lies in the peripheral direction of the coil and does not contribute to rotation of the rotor since the current vector in this direction only generates a torque displacing the coil upwards or downward. Besides the effective torque is not lowered since said four triangles cancel the torque of each other completely to dissipate the movement in the vertical direction.

The current vector in the two rhombs lies in a direction perpendicular to the periphery of the coil, and a rotational torque is generated by means of Flemings left hand rule when said current vector crosses the magnetic flux. Though the current vectors in these two blocks are in opposite directions, direction of torque is directed in the same direction since the directions of magnetic flux are inverted in these two blocks.

FIG. 4A shows another example, in which the length of parallel conductors is doubled in comparison with the case of FIG. 2 and the flexible sheet is folded three times along the lines A A, B B and C C to obtain a 4-ply folded sheet for making double-layer rolled structure as shown in FIG. 4B. Thus, the number of conductors can be easily increased by such double or triple layer structure, while the accomodatable number in a single-layer structure is limited. Said triple layer structure can be made similarly to the double layer structure, except that the length of parallel conductors on said parallelogram (that is, longitudinal length of the parallelogram) is tripled and the flexible sheet is folded into a 6-ply folded sheet. In case of multiple-layer structure, however, it might become difficult to made connections between the ends of said conductors'because of difference in peripheral length in' the inner layer and outer layer. Besides, in case of doubling the length of said parallel conductors, it becomes necessary to cut off the extended portion of the n-th conductor as shown in FIG. 4, since otherwise the connections between the corresponding ends will not give a serially connected circuit but lead only to n rings such as l- (l), 2 (2), Furthermore, the example of FIG. 4 economizes the soldering operation since the whole circuit is completed by means of soldering at one portion regardless of the number of folding. 1

The example shown in FIG. 5 is similar to the embodiment in FIG. 2 in that the flexible sheet is folded at the line A A and is rolled up to make a single-layer structure in which the point 1 for example is connected to the point n l but different therefrom in that the loop to be formed in this case by connecting the corresponding ends of conductors on said folded flexible sheet has a structure that a conductor makes three cycles across said folded sheet until it makes a full turn around the periphery of the rotor where it is connected to the adjacent conductor, due to steeper inclination of the parallel conductors. In this case, however, a circuit connected in series cannot be obtained if the number of conductors is a multiple of 3.

In case the conductor makes 3 cycles while it goes around the periphery of the rotor, the number of conductors should therefore be 3n i 1, wherein n is an integer, in order that the connection to a conductor adjacent to the previous one forms a wholly serial circuit. Similarly the number of conductors should be 2n 1, 4n 1 I or mn i 1 if a conductor is to make 2, 4 or m cycles across said folded sheet, respectively, and any desirable number of cycles across the folded sheet can be realized in a similar manner.

FIG. 6 shows theexplanation, in developed form, of the working principle of a motor provided with the structure shown in FIG. 5. Similar to the case of FIG. 3, the rotor can be divided into rhombs and isosceles triangles, which are separated from each other by means of diagonally disposed conductors ending at or starting from the contact points of brushes. In this case, 6 rhombs and 12 isosceles triangles are obtained since the conductor makes three cycles across the width of said folded sheet while making a full turn around the periphery of the rotor as shown in FIG. 6 in contrast to one cycle in FIG. 3. It is already explained in connection with FIG. 3 that said rhombs effectively generate the rotational power while said triangles are ineffective. It is to be noted, however, that the current vectors in said six rhombs are in opposite directions alternatively, and the magnet should therefore be magnetized accordingly in six poles as shown in FIG. 6.

A comparison of FIG. 3 with FIG. 6 may lead to a conclusion that two motors of the same dimension but produced according to these two different examples as above respectively will generate the same torque, since the total area of rhombs contributing to the torque generation is the same and equal to a half of the total area of the coil in both cases, despite the difference in number of rhombs, two and six respectively. However, it should be noted that, with vertically more oblong rhombs in the case of FIG. 6, a given current in the conductors in the case of FIG. 6 will give a larger vector length, signifying higher efficiency for producing the torque.

Besides, it is naturally preferable to make as many cycles of electric current as possible across said folded sheet during a full turn of electric current around the rotor, and the conductors with steeper inclination shown in FIG. 5'are therefore more advantageous than those in FIG. 2 with less inclination for a given width of the folded sheet, since the former disposition allows a larger number of conductors on said sheet. This structure, however, has limitations as to the mechanical strength of the cylindrical rotor to be formed therefrom because the adhering area is reduced in making the cylindrical shape, and also as to magnetization of the magnet, which is required to have poles equal to twice the number of said cycles.

The motor according to this invention, of which the working principle has been clarified in the foregoing explanation, is further provided with advantages, compared with other motors, with respect to the production process thereof. Though the printed circuit sheet employed in this invention has a shape of a parallelogram, it will readily be understood that said sheet can be cut from a long strip of a constant width in which parallel conductors are provided uniformly. Stated differently said sheet can be produced by applying the steps of photosensitive material coating, drying, exposure, development, etching, washing and cutting continuously on a long strip of a flexible sheet for printed circuit, with fully automated process control if desirable.

Furthermore said sheet, because of simple structure thereof consisting solely of parallel conductors, can also be prepared by adhering or embedding thin copper sheet slitted beforehand into a desirable width directly on a thin plastic sheetinstead of using a printed circuit sheet prepared according to the procedure mentioned above, and the parallelogram in which parallel conductors are provided can be obtained simply by cutting said thin plastic sheet.

From the standpoint of production, an example shown in FIG. 7, in which the parallelogram is divided into the inner and outer pieces of half the original size provided respectively with the inner part and outer part of the coil, is preferred to the foregoing examples employing folded parallelogram.

In the foregoing examples employing a folded sheet,

' the width of the conductors and the clearance therebetween should be large enough so as to ensure appropriate connections between the respective end edges of said conductors, since the conductors constituting the inner part of the coil are arranged with dimensions identical with those of conductors constituting the outer part of the coil and this fact tends to show aberration in pitch of the conductors'of the inner part and of the outer part when the sheet is rolled up to form a cylinder, even if such aberration is not observable when the sheet is extended. Such widening of said width or interval is undesirable, leading to the decrease of number of conductors and eventually to the loss of the efficiency of motor.

On the other hand, in case the parallelogram is divided into two pieces, a piece of a length of L and that of L a (a is equal to the thickness of printed circiut sheet times 1r) can be easily obtained by slightly changing the angle of cutting said pieces from a mother sheet as shown in FIG.7A. By utilizing said pieces of a length of L and of L a for the inner and outer parts respectively, it is possible to prevent said aberration and thus it is also possible to reduce the width of conductors and clearance therebetween.

It is already explained that the structure shown in FIG. 5, when a conductor makes an elevated number of cycles across the folded sheet, will give rise to reduced mechanical strength due to the restriction on the adhering area. In contrast thereto, two separate pieces employed in this example can be arbitrarily displaced from each other in the lateral direction as shown in FIG. 7B, thus providing a larger adhering area and higher mechanical strength and further to realize an exactly circular shape by disposing the joints of outer piece and inner piece in opposite positions with respect to the center of rotor.

In case of .using divided two pieces the connections of conductors should be made both at the upper and lower extremities of the cylinder, whilethe folded sheet requires the connection solely at the lower extremity. However this fact will not be any serious problem in the production process since such connections can be easily realized by dipping said extremities of the cylinder into moltensolder, so long as the ends of conductors are correctly disposed in corresponding positions.

This example can also be extended to multi-layer structure by employing pieces of a length of L, L a, L 2a, L 30:, successively from the innermost layer.

Thus the process of this invention poses no limitation on the thickness, width and distance of the conductors, and therefore can be applied in the same manner to the motors of various powers rangingfrom several watts to several kilo-watts.

Besides, it will be readily understood that the present invention is applicable not only to motors but also to various generators.

Thus this invention has enabled the manufacture of various motors and generator of very high efficiency by means of a simple process, and therefore is of a great industrial value.

What I claim is:

l. A process for producing a cylindrical rotor which comprises the steps of providing an elongated strip of flexible insulative film with a number of mutually insulated parallel conductors with a regular interval on one surface thereof, each of said conductors extending along a straight line generally paralleling opposite longitudinal edges of said strip, cutting said strip along two parallel lines intersecting said longitudinal edges at an acute angle to form a parallelogram wherein said con ductors terminate flush with the cut edges, folding back said parallelogram on itself with said conductors on the outer surfaces thereof to obtain a trapezoidal folded sheet with the ends of said conductors all lying on a single edge of the trapezoid, rolling up said trapezoidal folded sheet to obtain a cylinder with the ends of said conductors all lying on the periphery of one end of the cylinder, and connecting the corresponding ends of said conductors on said sheet by soldering the ends of the conductors on one side of the sheet directly to the ends of the conductors on the other side of the sheet.

2. A process according to the claim I wherein said parallelogram is folded into an even number of plies.

3. A process according to claim 1, wherein said parallel conductors are embedded in a flexible insulative film at regular intervals.

4. A process for producing a cylindrical rotor which comprises the steps of providing a number of mutually insulated parallel conductors with a regular interval on one surface of a sheet of flexible insulative film, each of said conductors extending along a singlestraight line generally paralleling opposite longitudinal edges of said sheet, cutting a plurality of parallelograms from said sheet along paired lines intersecting the longitudinal edges at acute cutting angles, said conductors terminating flush with opposite cut edges of each parallelogram, the length of said parallelograms along the cut edges being stepwise increased by means of changing the cutting angle of said film, superimposing said parallelograms on each other in the order of the different lengths thereof with the conductors on adjacent sheets intersecting each other with a layer of said insulative film therebetween, rolling said superimposed parallelograms into a cylinder with the longer parallelogram on the outer surface thereof and with the ends of said conductors all lying on the peripheries of the ends of the cylinder, and connecting the corresponding ends of said conductors at both ends of said cylinder by soldering the ends of the conductors on one side of each sheet directly to the ends of the conductors on the other side of the sheet.

5. A process according to claim 4, wherein said parallel conductors are embedded in a flexible insulative film at regular intervals.

6. A process for producing a cylindrical rotor which comprises the steps of providing a sheet of insulative film having a pair of opposite longitudinal parallel edges, forming a number of mutually insulated parallel conductors at a regular interval on one surface of said sheet running generally parallel to the longitudinal to obtain a cylinder with the ends of said conductors all lying on the periphery of one end of the cylinder, and connecting the corresponding ends of said conductors on said sheet by soldering the ends of the conductors on one side of the sheet directly to the ends of the conductors on the other side of the sheet. 

1. A process for producing a cylindrical rotor which comprises the steps of providing an elongated strip of flexible insulative film with a number of mutually insulated parallel conductors with a regular interval on one surface thereof, each of said conductors extending along a straight line generally paralleling opposite longitudinAl edges of said strip, cutting said strip along two parallel lines intersecting said longitudinal edges at an acute angle to form a parallelogram wherein said conductors terminate flush with the cut edges, folding back said parallelogram on itself with said conductors on the outer surfaces thereof to obtain a trapezoidal folded sheet with the ends of said conductors all lying on a single edge of the trapezoid, rolling up said trapezoidal folded sheet to obtain a cylinder with the ends of said conductors all lying on the periphery of one end of the cylinder, and connecting the corresponding ends of said conductors on said sheet by soldering the ends of the conductors on one side of the sheet directly to the ends of the conductors on the other side of the sheet.
 2. A process according to the claim 1 wherein said parallelogram is folded into an even number of plies.
 3. A process according to claim 1, wherein said parallel conductors are embedded in a flexible insulative film at regular intervals.
 4. A process for producing a cylindrical rotor which comprises the steps of providing a number of mutually insulated parallel conductors with a regular interval on one surface of a sheet of flexible insulative film, each of said conductors extending along a single straight line generally paralleling opposite longitudinal edges of said sheet, cutting a plurality of parallelograms from said sheet along paired lines intersecting the longitudinal edges at acute cutting angles, said conductors terminating flush with opposite cut edges of each parallelogram, the length of said parallelograms along the cut edges being stepwise increased by means of changing the cutting angle of said film, superimposing said parallelograms on each other in the order of the different lengths thereof with the conductors on adjacent sheets intersecting each other with a layer of said insulative film therebetween, rolling said superimposed parallelograms into a cylinder with the longer parallelogram on the outer surface thereof and with the ends of said conductors all lying on the peripheries of the ends of the cylinder, and connecting the corresponding ends of said conductors at both ends of said cylinder by soldering the ends of the conductors on one side of each sheet directly to the ends of the conductors on the other side of the sheet.
 5. A process according to claim 4, wherein said parallel conductors are embedded in a flexible insulative film at regular intervals.
 6. A process for producing a cylindrical rotor which comprises the steps of providing a sheet of insulative film having a pair of opposite longitudinal parallel edges, forming a number of mutually insulated parallel conductors at a regular interval on one surface of said sheet running generally parallel to the longitudinal edges thereof, cutting said sheet along two parallel lines intersecting said longitudinal edges at an acute angle to form a parallelogram wherein said conductors terminate flush with the cut edges, folding back said parallelogram on itself with said conductors on the outer surfaces thereof to obtain a trapezoidal folded sheet with the ends of said conductors all lying on a single edge of the trapezoid, rolling up said trapezoidal folded sheet to obtain a cylinder with the ends of said conductors all lying on the periphery of one end of the cylinder, and connecting the corresponding ends of said conductors on said sheet by soldering the ends of the conductors on one side of the sheet directly to the ends of the conductors on the other side of the sheet. 